Use this free web calculator to estimate your COMAH liability. It may be useful for sites wondering whether they are in COMAH, or trying to assess whether they can avoid COMAH.

This calculator only provides an estimate, and not a full COMAH calculation, as Named Substances are not included. This means it can tell you if you are in COMAH, but may give an underestimate if you get a result which says you are not in COMAH. If you do need a full COMAH calculation package, look at our SEvaluate™ program.

How to use the calculator

Next to each COMAH/ Seveso category, simply type in the tonnage of that material stored, made or handled on site at any one time. The result will automatically be updated at the bottom of the page.

Disclaimer: this calculator will only give you an idea of COMAH liability, as it does not include Named Substances, and is therefore likely to be an underestimate. The results depend on you entering your inventory quantities accurately. This web calculator is only for indicative purposes, and not for regulatory purposes. No liability can be accepted for errors, miscalculations, underestimates or overestimates based on the use of this calculator, or for use for regulatory purposes. Use of the calculator implies that you agree to these conditions.

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  • The calculator only works for a single site at any one time, although you can clear the data and re-input for a different site (use the cancel button at the bottom of the page).
  • To print your results, use the print button in the calculator rather than the print page function in your browser.
  • We have not included Named Substances because of space; this facility is included in our commercial product, SEvaluate™. You can always calculate your Named Substance liability manually to provide a full view of your current COMAH liability.
  • For COMAH/SEVESO purposes, the mass of a complete product is included in the calculation (unlike REACH which ignores water). This is because the hazard is from the product as a whole.  For more details of this and other COMAH calculation FAQs, we recommend you download COMAH liability toolkit, details below.
  • If the calculator doesn’t work properly on your mobile phone:
Download our free Android app or scan the QR code; Android SevEstimateDownload the Android App
Download the iPhone and Windows app or scan the QR code; iphone SevEstimate
Download iPhone & Windows App

If you have any other questions about using the SevEstimate™ calculator, email us on . This calculator is provided as a service to industrial/ professional users only.

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COMAH Liability Toolkit toolkit

The COMAH liability toolkit contains 5 useful documents:
  • COMAH Factsheet
  • COMAH Calculation Factsheet
  • Top 16 COMAH calculation mistakes
  • When to notify under COMAH 2015-16
  • Should you control your inventory to avoid COMAH or stay in Lower Tier?
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SevaluateTM is an Excel based program which runs your COMAH (Seveso III) calculations for you, provides printable reports showing the main contributors to your COMAH liability, and allows you to predict the impact of changing your COMAH inventory on your COMAH liability.
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